Overload current protection apparatus

ABSTRACT

A current sensor which constitutes an overload protection apparatus and senses a current supplied from a power source to a load is constituted by providing a magnetic sensor having the effect of magnetic impedance (MI), an AC supply means which impresses AC on this sensor, a bias current supply means which supplies a bias current to a bias coil, a peak sensing means which senses the peak or a change in impedance of the magnetic sensor as a change in voltage, and a switch which selects the output of the peak sensing means in accordance with each phase. A holding means which holds switch outputs one after another and an amplification means are provided in common to enable current sensing for each phase. Thus, a range of current sensing is enlarged to reduce power consumption and cost.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to an over-current protectiondevice for detecting a current flowing through a conductor and forshutting oft the current when the current exceeds a predeterminedthreshold value. More particularly, the present invention relates to anover-current protection device capable of controlling power supplied toa load such as an electric motor.

DESCRIPTION OF TECHNICAL BACKGROUND

[0002] An over-current protection device detects a current flowingthrough a load such as a three-phase motor via a contactor, and shutsoff the current flowing to the motor when the current exceeds a safethreshold value. Conventionally, such a device is provided with abi-metal switching element, and a part or all of the current to themotor flows through the bi-metal switching element. That is, the currentflows though a switch consisting of the bi-metal element so that thebi-metal element is heated according to an intensity of the current.When the motor current exceeds a sate threshold value for a period oftime longer than a predetermined time, the bi-metal element bends due tothe heat to hold a switch contact in an open state, thereby shutting offthe power to a control input terminal of a contactor. However, in thedevice using the bi-metal switch, it is difficult to adjust the currentin the state that the switch is opened, so that the incorrectly adjustedcondition tends to continue for a long time.

[0003] On the other hand, when an electric device is used instead of thebi-metal element, it is possible to electronically perform the functionof the bi-metal switch. Accordingly, it is possible to improvereliability and easily adjust the device. However, the electronic deviceincludes a complex circuit, and in order to properly detect a current tooperate a contactor, it is necessary to provide a constant-voltage powersupply and a large number of components. In addition, a currentdetection transformer has been used as a device for detecting current.Accordingly, it is difficult to obtain a wide range for detecting acurrent due to magnetic saturation of an iron core. It is possible toprovide a magnetoresistive element as a device for detecting a current.However, it is necessary to provide an iron core due to a lowsensitivity of the magnetoresistive element. Accordingly, similar to thecurrent detection transformer, it is difficult to obtain a wide rangefor detecting a current.

[0004] To solve these problems, as a high sensitive magnetism detectionelement for replacing a Hall element and the magnetoresistive element, amagnetic impedance element using an amorphous wire has been disclosed(refer to Patent Document 1) Further, an amorphous magnetic thin filmformed via a sputtering method has been used (refer to Patent Document2).

[0005] When one of the magnetic impedance elements is used, it ispossible to obtain high sensitivity in the magnetism detectioncharacteristic. However, as shown in FIG. 17, impedance changesnon-linearly relative to a magnetic field of the amorphous wire element,so that the magnetic impedance element has a non-linear output of themagnetism detection characteristic (refer to Patent Document 3).Accordingly, the linear output relative to the magnetic field isobtained from a difference in a variation of the magnetic impedanceelement obtained from a sum of the positive and negative magnetic fieldsgenerated by the AC bias magnetic field and the immeasurable externalmagnetic field, so that an AC bias magnetic field is applied to themagnetic impedance element (refer to Patent Document 4).

[0006] [Patent Document 1]

[0007] Japanese Patent Publication (Kokai) No. 06-281712

[0008] (page 4, FIG. 5 to FIG. 12)

[0009] [Patent Document 2]

[0010] Japanese Patent Publication (Kokai) No. 08-075835

[0011] (pages 4 to 5, FIG. 1 to FIG. 6)

[0012] [Patent Document 3]

[0013] Japanese Patent Publication (Kokai) No. 2000-055996

[0014] (page 3, FIG. 23)

[0015] [Patent Document 4]

[0016] Japanese Patent Publication (Kokai) No. 09-127218

[0017] (pages 4 to 5, FIG. 3)

[0018] Incidentally, in principle, the magnetic impedance elementgenerates a magnetic impedance effect. Accordingly, it is necessary toapply a high-frequency current of several mA and at least several MHz tothe element, thereby increasing the power consumption and a size of thepower-supply transformer, and making it difficult to downsize the deviceand reduce cost of the device.

[0019]FIG. 16 shows an example of a conventional detecting circuit usingthe magnetic impedance element. The circuit includes sheared oscillatingmeans 31 and bias-current applying means 13 a 1. A current of several mAand a bias current of about several tens of mA are constantly applied tomagnetism detection elements 1 a, 1 b, and 1 c, thereby increasing thepower consumption in proportion to the number of the elements. Further,it is necessary to provide wave detection means 6 a 1, 6 b 1, and 6 c 1;holding means 8 a 1, 8 b 1, and 8 c 1; and amplifying means 11 a 1, 11 b1, and 11 c 1 in proportion to the number of the magnetism detectionelements, thereby increasing la size of the circuit and cost of theparts.

[0020] In view of the problems, the present invention has been made, andan object of the present invention is to provide an over-currentprotection device with a compact and low cost configuration having alow-cost power-supply source in which a constant-voltage regulatedpower-supply is not necessary. Further, it is possible to obtain a widerange of the current detection.

SUMMARY OF THE INVENTION

[0021] To solve the problems described above, according to a firstaspect of the present invention, an over-current protection device forshutting off power supply to a load when an over-loaded-current isgenerated includes a switching unit for switching a current suppliedfrom a power-supply source to the load; a current detector for detectingthe current supplied from the power-supply source to the load; and acontrolling power-supply source for supplying power to each of thecomponent elements. The current detector includes a magnetism detectionelement corresponding to a phase of the power-supply source and having amagnetic impedance effect; AC-current supply means for supplying an ACcurrent to the magnetism detection element via oscillating means and afirst switch corresponding to the magnetism detection element;bias-current supply means formed of a bias coil wound on the magnetismdetection element, a third switch, and bias-current applying means forsupplying a current to the bias coil via the third switch; wavedetection means corresponding to the magnetism detection element forconverting an individual impedance variation into a voltage and forpassing a peak of the converted voltage the wave detection means; asecond switch corresponding to the wave detection means for selecting anoutput of the wave detection means; holding means for holding theselected output of the wave detection means; and amplifying means foramplifying the voltage held by the holding means. It is possible todetect the current for each phase based on the selective operation ofthe first through third switches.

[0022] According to a second aspect of the present invention, anover-current protection device for shutting off power supply to a loadwhen an overloaded current is generated includes a switching unit forswitching a current supplied from a power-supply source to the load; acurrent detector for detecting the current supplied from thepower-supply source to the load; and a controlling power-supply sourcefor supplying power to each of the component elements. The currentdetector includes a magnetism detection element having a magneticimpedance effect and corresponding to a phase of the power-supplysource; AC-current supply means for supplying an AC current to themagnetism detection element via oscillating means and a first switchcorresponding to the magnetism detection element; bias-current supplymeans formed of a bias coil wound on the magnetism detection element,bias-current applying means, and dividing means connected to theoscillating means via a third switch for dividing a signal output fromthe oscillating means for feeding a current having a different polarityto the bias coil based on first and second timings; wave detection meanscorresponding to the magnetism detection element for converting animpedance variation into a voltage and for passing a peak of thevoltage; a second switch corresponding to the wave detection means forselecting a signal output from the wave detection means; a first holdingmeans for holding the selected signal output from the wave detectionmeans; a pair of fourth switches for selecting the held voltage based onthe first and second timings; a pair of second holding means for holdingthe selected two voltages; and amplifying means for amplifying adifference in the signals output from the pair of the second holdingmeans. It is possible to detect the current for each phase based on theselective operation of the first through fourth switches.

[0023] In the first and second aspects of the present invention, whenthe first switch and the second switch corresponding to the magnetismdetection element disposed in the phase of the power-supply source areselected, it is possible to select the third switch (according to athird aspect of the present invention). Alternatively, it is possible tooperate the oscillating means synchronous with the third switch(according to a fourth aspect of the present invention).

[0024] In the first and second aspects of the present invention, thecontrolling power-supply source may include at least a pair ofpower-supply transformers having a primary coil and a secondary coil andconnected to a current supply line from the controlling power-supplysource to a load; a storage battery for storing the current at asecondary side; and a voltage adjuster (according to a fifth aspect ofthe present invention). Alternatively, the controlling power-supplysource may include a power-supply transformer having at least a pair ofprimary coils and a secondary coil and connected to a current supplyline between the power-supply source and the load; a storage battery forstoring the current at a secondary side; and a voltage adjuster(according to a sixth aspect of the present invention). In the sixthaspect of the present invention, at least a pair of the primary coilsand the secondary coil may be wound on a single iron core, and theprimary coils may have different winding turns according to the phase(according to a seventh aspect of the present invention). In the seventhaspect of the present invention, a pair of the primary coils provided inthe power-supply transformers may have a winding ratio of 1:2 (accordingto an eighth aspect of the present invention).

[0025] Further, in the first and second aspects of present invention, itis possible to integrate the magnetism detection element, a terminalsfor applying an AC current to the magnetism detection element, the biascoil, and a terminal for feeding a bias current to the bias coil with aresin molding process (according to a ninth aspect of the presentinvention). Alternatively, it is possible to integrate the magnetismdetection element, a terminal for applying an AC current to themagnetism detection element, the bias coil, a terminal for feeding abias current to the bias coil, and a circuit for outputting a signalproportional to the signal output from the magnetism detection elementwith a resin molding process (according to a tenth aspect of the presentinvention). Alternatively, it is possible to use a thin-film device asthe magnetism detection element (according to an eleventh aspect of thepresent invention).

[0026] That is, in the present invention, the magnetism detectionelement having the magnetic impedance (MI) effect is used as the currentdetection means to prevent magnetic saturation caused by an iron core ina widely used conventional current detection transformer, therebyincreasing a range of the current detection. Further, the controllingpower-supply source does not need external power supply from aconstant-voltage regulated power source. As a result, it is possible toprovide an over-current protection device having wide applicability andis capable of decreasing the total cost.

[0027] When a multi-phase AC power-supply source is used, it is notnecessary to provide a power-supply transformer for each phase, therebyproviding the over-current protection device with a smaller number ofparts and low cost. In this case, the oscillating means is a single unitinstead of several oscillating means for each phase in the conventionalmethod. It is possible to apply the AC current to the elements anddevices disposed for each phase only when selected. Accordingly, it ispossible to decrease power consumption. When the power is supplied tothe bias coils only upon the detection, it is possible to further reducethe power consumption is further lowered by solely. When the oscillatingmeans is operated only upon the detection, it is possible to furtherreduce power consumption.

[0028] Further, it is possible to provide only a single system of theholding means and the amplifying means, thereby further reducing powerconsumption and cost. The positive and negative bias magnetic fields arealternately applied to the magnetism detection element, and a differencein the detected voltages at the time of applying the bias magnetic fieldis determined. Accordingly, it is possible to improve linearity or theoutput. Further, a pulse is used to drive intermittently in place of theconventional AC biasing system, thereby further reducing powerconsumption.

[0029] In addition, the magnetism detection element, AC-current inputterminal thereof, bias coil, and current input terminal thereof areintegrated with a resin molding process, thereby decreasing the magneticresistance and bias current and reducing a size. Further, the magnetismdetection element, AC-current input terminal thereof, bias coil, currentinput terminal thereof, and circuit for outputting a signal proportionalto the signal output from the magnetism detection element areintegrated, thereby improving the S/N (signal-to-noise) ratio. Inparticular, various corrective data are incorporated in the system toimprove the function thereof, thereby obtaining excellent environmentalresistance, high precision, and lower power consumption. The thin-filmdevice is used as the magnetism detection element, thereby eliminatingthe adverse influence of variable output caused by a strain in thewire-type element and reducing power consumption with high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a schematic block diagram of an over-current protectiondevice according to a first embodiment of the present invention;

[0031]FIG. 2 is a schematic view of a magnetism detection unit;

[0032]FIG. 3a is a schematic block diagram of a first embodiment of amagnetism detection unit;

[0033]FIG. 3b is a time chart showing an operation of each of switchesshown in FIG. 3a;

[0034]FIG. 3c is an explanatory view of an operating timing ofoscillating means;

[0035]FIG. 3d is a partial view showing a modified example of themagnetism detection unit shown in FIG. 3a;

[0036]FIG. 3e is a time chart showing an operation of the modifiedexample shown in FIG. 3d;

[0037]FIG. 4 is a schematic block diagram showing individual componentsshown in FIG. 3a;

[0038] FIG. b is a schematic block diagram of a second embodiment of themagnetism detection unit;

[0039]FIG. 6 is an explanatory view showing positive and negativebiases;

[0040]FIG. 7 is a schematic block diagram showing individual componentsshown in FIG. 5;

[0041]FIG. 8 is a view showing a circuit of another embodiment of theoscillating means;

[0042]FIG. 9 is a schematic block diagram of an over-current protectiondevice according to a second embodiment of the present invention;

[0043]FIG. 10 is a view showing a constitution of a transformer;

[0044]FIG. 11 is a perspective view showing a constitution of a magneticsensor;

[0045]FIG. 12 is an explanatory view showing a process of producing themagnetic sensor shown in FIG. 11;

[0046]FIG. 13 is an explanatory view showing an assembled state of theloaded magnetic sensor shown in FIG. 11;

[0047]FIG. 14 is an explanatory view showing an example of a magneticshielding;

[0048]FIG. 15 is a perspective view showing an example of the magnetismdetection unit;

[0049]FIG. 16 is a schematic block diagram of a conventional magnetismdetection unit; and

[0050]FIG. 17 is an explanatory view showing magnetic impedancecharacteristic of an amorphous wire.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] Hereunder, the present invention will be described. FIG. 1 is aschematic block diagram of an over-current protection device accordingto a first embodiment of the present invention.

[0052] In FIG. 1, power-supply lines R, S, and T connected to athree-phase AC power-supply source (not shown) are linked with a motor30 via a three-phase contactor 20 and a pair of power-supplytransformers 161 and 162. A current detection unit 11 detects a currentsupplied via the power-supply lines R, S, and T for each phase. Evenwhen one of the three phases incurs disconnection, it is required thatthe entire system be operated normally. Accordingly, the embodimentincludes a pair of power-supply transformers 161 and 162. However, thetransformer may be disposed for each phase. The contactor 20 has threecontacts 201, 202, and 203, and each of the contacts is directlyconnected to the motor 30, or individually connected via primary coilsof the power-supply transformers 161 and 162 through the power-supplylines R, S, and T. The three contacts are mechanically united with eachother, so that an electromagnetic coil 204 connected to a controlcircuit 10 can drive the three contacts simultaneously. Theabove-mentioned current detection unit 11, a pair of power-supplytransformers 161 and 162, and the control circuit 10 constitute anelectronic overload relay unit 1. A current regulator (gain adjuster)100 amplifies a signal output from the current detection unit 11 incorrespondence with a preset current value. The signal output from thecurrent detection unit 11 is sent to an analog input of a microcomputer(mi-con) 102 via a half-wave rectifier 101.

[0053] In the controlling power-supply source shown in FIG. 1, a firstcapacitor 180 is connected to the secondary coils of the power-supplytransformers 161 and 162 via a pair of rectifying diodes 171 and 172.Protecting diodes 174 and 175 are respectively linked between an anodeand a ground of the circuit. The first capacitor 180 is linked between apositive input of a voltage adjuster 19 and the ground of the circuit. Asecond capacitor 181 is linked between a positive output and the groundof the circuit, so that the voltage adjuster 19 to output a constantvoltage level VCC as a power-supply source of the electronic overloadrelay unit 1.

[0054]FIG. 2 is a view showing a configuration of a current detectionunit. Reference numeral 111 shown in FIG. 2 designates a magneticimpedance element (MI element), 122 designates a wiring for supplying acurrent to each phase, 121 designates a substrate for fixing the wiringand the MI element 1, and 110 designates a detection circuit.

[0055] The MI element 111 may include one formed of an amorphous wiredisclosed in Japanese Patent Publication (Kokai) No. 06-281712, and athin film device disclosed in Japanese Patent Publication (Kokai) No.08-075835. FIG. 2 shows the MI element corresponding to a single phase,and each phase has an identical constitution.

[0056]FIG. 3a is a view showing a first embodiment of the currentdetection unit. Reference numerals 1 a, 1 b, and 1 c respectivelydesignate an MI element formed in a wire shape or a thin-film. Referencenumerals 2 a, 2 b, and 2 c respectively designate a bias coil forfeeding a bias to the MI elements 1 a, 1 b, and 1 c. Reference numeral 3designates an oscillating circuit. Reference numerals 4 a, 4 b, and 4 crespectively designate a first switch. The first switches 4 a, 4 b, and4 c individually switch a signal output from the oscillating circuit 3,and then apply a high-frequency AC current to the MI elements 1 a, 1 b,and 1 c. Reference numeral 13 a designates second current-applying meansfor feeding a current to the bias coils 2 a, 2 b, and 2 c, and a thirdswitch 14 a turns on and off the current. Reference numerals 6 a, 6 b,and 6 c respectively designate wave-detecting means for outputting apeak value of varied impedance of the MI elements 1 a, 1 b, and 1 cconverted into varied voltages. Reference numerals 7 a, 7 b, and 7 crespectively designate a second switch for extracting a signal outputfrom the wave detection means in correspondence with the selected MIelement. Reference numeral 8 a designates first holding means forholding the signal output from the wave detection means 6 a, 6 b, and 6c. Reference numeral 11 a designates amplifying means for amplifying thesignal output from the first holding means 8 a.

[0057] In response to the control signals A1, A2, B1, B2, C1, and C2 forthe first switches 4 a, 4 b, and 4 c and the second switches 7 a, 7 b,and 7 c, the microcomputer 102 selects one of the MI elements 1 a, 1 b,and 1 c, and further outputs a control signal El for delivering a biascurrent.

[0058] More particularly, in response to the control signals A1 or A2,the MI element 1 a is selected. Likewise, in response to the controlsignals B1 or B2, the MI element 1 b is selected. Likewise, in responseto the control signals C1 or C2, the MI element 1 c is selected. Inaddition, in response to the control signal E1, a bias current isdelivered to one of the MI elements 1 a, 1 b, and 1 c. Accordingly, itis possible to apply the AC current and bias current to the MI elementsconsuming the majority of power solely for a period of time when thecontrol signal is, thereby reducing the consumed power. For example,when the MI element 1 a is driven, the first switch 4 a and secondswitch 7 a are turned on at substantially the same time, and the controlsignal E1 is simultaneously output only once to turn on the third switch14 a, thereby reducing power consumption. Further, the first holdingmeans 8 a and the amplifying means 11 a can be constituted in a singlesystem, thereby further facilitating power consumption and lower cost.

[0059] In terms of the timing after the MI element 1 a is operated, thefirst switch 4 b and second switch 7 b are turned on at substantiallythe same time. The control signal E1 is simultaneously output only onceto turn the third switch 14 a on, thereby turning on the MI element 1 bto further turn on the first switch 4 c and the second switch 7 c atsubstantially the same time. Simultaneously, the control signal E1 isoutput only once to turn on the third switch 14 a, thereby activatingthe MI element 1 c. FIG. 3b is a timing chart showing the abovesequential operations.

[0060] As shown in FIG. 3c, the oscillating means 3 is activated basedon the timing of operating the third switch in response to the controlsignal E1. Accordingly, the oscillating means 3 can execute anoscillating operation only when a bias current is fed to the bias coils2 a, 2 b, and 2 c. As a result, as compared with a case that theoscillating means 3 continuously executes the oscillating operation, itis possible to further reduce power consumption.

[0061]FIG. 3d shows a modified example of the device shown in FIG. 3a.The holding means 8 a is provided in common with the wave detectionmeans 6 a, 6 b, and 6 c shown in FIG. 3a. As shown in FIG. 3d, theholding means 8 c, 8 d, and 8 e is individually provided in the wavedetection means 6 a, 6 b, and 6 c, respectively. As in the case shown inFIG. 3a, the first switch and the third switch are turned on atsubstantially the same time. However, with the above arrangement, it ispossible to select the operating timing. Incidentally, the secondswitches 7 a, 7 b, and 7 c are integrated. FIG. 3e is a timing chart ofthe integrated unit.

[0062]FIG. 4 is a view showing an embodiment of the device shown in FIG.3a. The oscillating means 3 may include a quartz oscillator ortransistor, and in this embodiment, the oscillating means 3 is formed ofa CMOS gate as an example. The wave detection means 6 a, 6 b, and 6 cmay be formed of analog switches, and in this embodiment, the wavedetection means 6 a, 6 b, and 6 c are formed of diodes. The firstholding means 8 a is formed of a resistor and capacitor. The amplifyingmeans 11 a may be formed of a transistor, and in the embodiment, theamplifying means 11 a is formed of an operational amplifier as anexample. The first, second, and third switches are respectively formedof relays or analog switches. For the purpose of lowering the currentfed to the MI elements 1 a, 1 b, and 1 c, current limit resistors 5 a, 5b, and 5 c are provided. However, the current limit resistors may beomitted.

[0063] The diagrams shown in FIG. 3a and FIG. 4 can detect magnetismwith a simplified constitution. However, a variation in impedancerelative to a magnetic field of the amorphous wire elements exhibitsnon-linearity as shown in FIG. 17, so that the output precision is notsatisfactory.

[0064]FIG. 5 is a view showing a second embodiment with an improvementin the non-linear characteristic. As compared with that shown in FIG.3a, the positive and negative bias magnetic fields are alternatelyapplied to the MI elements 1 a, 1 b, and 1 c, so that a difference indetected voltages upon the application of the individual bias magneticfields is obtained, thereby improving the output linearity.

[0065] Reference numeral 12 designates frequency-dividing means fordividing a frequency of the signal output from the oscillating means 3.The dividing means 12 outputs a signal containing a frequency lower thanthat of the AC current fed to the MI elements 1 a, 1 b, and 1 c.Reference numeral 13 b designates second current-applying means foralternately applying positive and negative bias magnetic fields inresponse to the positive and negative output timings delivered from thefrequency-dividing means 12. The second current-applying means 13 bapplies the output signal of the oscillating means 3 divided by thefrequency-dividing means 12 via the third switch 14 b to the bias coils2 a, 2 b, and 2 c. Further, the device is provided with first holdingmeans 8 b for holding a voltage corresponding to a variation inimpedance caused by the positive and negative bias magnetic fields ofthe MI elements 1 a, 1 b, and 1 c; a pair of second holding means 10 aand 10 b for holding the voltage output from the first holding means 8 bbased on the positive and negative timings; a pair of fourth switches 9a and 9 b operated by the timings D1 and 2; and differential amplifyingmeans 11 b for differentially amplifying the voltage output from thesecond holding means 10 a and 10 b.

[0066]FIG. 6 is an explanatory view showing an operation of the positiveand negative biases. Note that the operating characteristic of thesensor (i.e. the MI elements) relative to the magnetic field shown inFIG. 6 is that in a conventional magnetic impedance element.

[0067] FIGS. 6(a) and (b) are explanatory views of the operatingcharacteristic when the bias magnetic field is added while the externalmagnetic field remains zero. FIG. 6(a) schematically shows the operatingcharacteristic when the bias magnetic field having an equal intensity ofthe positive and negative magnetic fields is added to a magneticimpedance element under the condition that no appreciable externalmagnetic field out of the measurable range is present. FIG. 6(a) alsoshows a portion representing a variation in impedance relative to avariation in the intensity of the external magnetic field, andvariations caused by the intensity of the bias magnetic field added tothe magnetic impedance element and the adding duration.

[0068] The impedance characteristic does not show a smooth curve in anarea in which the intensity of the external magnetic field remains zero.In general, the impedance characteristic becomes unstable at a pointwhere the polarity of the magnetic field changes. The blank circlesshown on the impedance-characteristic curves designate the impedancevalues acquired from the values of the maximum positive/negative biasmagnetic fields generated by the bias magnetic field that periodicallyoscillates the positive and negative magnetic fields with a rectangularwaveform. Based on the relationship between the values and thehigh-frequency current available for the driving applied to the magneticimpedance element, an output voltage can be obtained. The difference inoutput voltages between the two points is detected.

[0069] As a result, in a case of no appreciable external magnetic fieldat outside of the measurable range, the output voltages at two pointsare identical, i.e. no difference, so that the output becomes zero afterthe differential amplifying operation as shown in FIG. 6(b).

[0070] On the other hand, FIGS. 6(c) and (d) are views showing anoperation of applying the bias when a measurable external magnetic fieldexists.

[0071]FIG. 6(c) presents a schematic chart showing the characteristic ina case that positive magnetic field of AH is detected as the externalmagnetic field outside the measurable range. Blank circles shown on thecurves for designating the impedance characteristic respectivelyrepresent the impedance values obtained from the maximum values of thepositive and negative magnetic fields of bias. The blank circles shiftto the closed circles due to the influence of the external magneticfield AH. Relative to the closed circles at the positive side and thenegative side of the oscillating bias magnetic field, the polarity ofthe voltage is defined by the direction that a voltage valuecorresponding to the closed circles at the negative side changes theclosed circles at the positive side.

[0072] Accordingly, the difference in the output voltages (differentialoutput) becomes AV of the positive voltage. When an external magneticfield at outside of the measurable range AH is detected, as shown inFIG. 6(d), the output after the differential amplifying operation isobtained as A×AV, in which A is an amplifying rate of the differentialamplifier.

[0073] As described above, instead of the conventional AC bias driving,by intermittently driving the magnetic impedance elements with pulses asshown in FIGS. 6(a) and 6(c), it is possible to further reduce powerconsumption as compared with the conventional method of drivingcontinuously.

[0074]FIG. 7 is a view showing an example of the device shown in FIG. 5.In contrast with that shown in FIG. 4, the circuit shown in FIG. 7corresponds to that provided with second holding means 10 a and 10 b,differential amplifying means 11 b, and frequency-dividing means 12. Inthis example, the second holding means 10 a and 10 b are formed ofcapacitors. The differential amplifying means 11 b is formed of adifferential amplifier of an operational amplifier. Thefrequency-dividing means 12 is formed of a flip-flop.

[0075] In place of the oscillating means 3 shown in FIG. 4 and FIG. 7,as shown in FIG. 8, one (3 al) capable of oscillating only when thecontrol signal E1 remains at a High level may be used, so that the thirdswitch 14 b and the oscillating means 3 a 1 are turned on via the signalE1 only when one of the groups including the first switches 4 a, 4 b,and 4 c, and the second switches 7 a, 7 b, and 7 c corresponding to eachpower-source phase is turned on, thereby further reducing powerconsumption.

[0076] The above description refers to a case in which the three-phaseAC power-supply source is used. In a case of a single phase, only thesingle phase is considered to employ the invention.

[0077]FIG. 9 is a schematic block diagram of an over-current protectiondevice according to a second embodiment of the present invention.

[0078] The circuit shown in FIG. 1 requires the power-supplytransformers 161 and 162 corresponding to at least two phases. On theother hand, the circuit shown in FIG. 9 includes a single core 145 toreplace the primary coils 140 and 150 provided for each phase so as toreceive power from the secondary coil 146, thereby eliminating one ofthe two cores. Concretely, as shown in FIG. 10, the core 145 is formedof a toroidal core 145 a. A winding ratio between the primary coils 140and 150 is selected to be, for example, 1:2, so that a proper currentlevel is fed from the secondary coil 146. The winding turns of theprimary coils differ among individual phases, because if the windingturns are identical, it is not possible to detect a vacant phase.

[0079] In the controlling power-supply source, a first capacitor 180 islinked with the secondary coil 146 via a rectifying diode 176. Aprotective diode 177 is connected between the anode of the rectifyingdiode 176 and the ground of the circuit. The first capacitor 180 isconnected between the positive input terminal of the voltage adjuster 19and the ground of the circuit. The second capacitor 181 is connectedbetween the positive output terminal of the voltage adjuster 19 and theground of the circuit. The voltage adjuster 19 outputs a constantvoltage level VCC.

[0080] Other components shown in FIG. 9 are identical to those shown inFIG. 1, and descriptions thereof are omitted.

[0081] Referring to FIG. 11, a concrete constitution of the magneticsensor as described above is described below.

[0082] In FIG. 11, reference numeral 111 designates a magnetismdetection element formed of a thin-film, and reference numeral 115designates a resinous bobbin formed on an outside surface of themagnetism detection element 111 with an insert-molding process.Reference numeral 116 designates a coil for applying a bias magneticfield to the magnetism detection element 111, reference numeral 117designates a coil for applying a negative feedback magnetic field to themagnetism detection element 111, and reference numeral 118 designates aresin case for protecting the magnetism detection element 111 and thecoils 116 and 117 from environmental hazards formed with aninsert-molding process. Reference numeral 114 designates terminals forapplying a high-frequency current to both ends of the magnetismdetection element 111, and for applying a current to the coils 116 and117. The entire constitution of the magnetic sensor is designated byreference numeral 120. In the constitution shown in FIG. 11, the coil isprovided for applying the negative-feedback magnetic field to themagnetism detection element 111. However, the coil may be omitted.

[0083]FIG. 12 is a view showing a process of assembling a magneticsensor unit. Initially, as shown in (2), a magnetism detection element111 is bonded between a pair of terminals on the lead frame 119 shown in(1). The bonding method includes a soldering process, an adhesiveprocess, and bonding. Next, as shown in (3), a bobbin 115 is integrallymolded with the lead frame 119 with the magnetism detection element 111.Next, as shown in (4), after the lead frame 119 is cut off, a bias coil116 and a negative feedback coil 117 are wound. Next, as shown in (5), acase 118 is molded directly above the coil unit. Next, as shown in (6),terminals 114 are folded to complete the assembly work.

[0084] It is possible to form the thin-film magnetism detection elementinto a substantially 1 mm square shape. Accordingly, it is possible toform the magnetic sensor 120 into a substantially 5 mm square shape,thereby decreasing the magnetic resistance between the magneticdetection element 111 and the coils 116 and 117.

[0085]FIG. 13 shows an example of the magnetic sensor in a mountedstate, wherein FIG. 13(a) is a perspective view thereof and FIG. 13(b)is a plan view thereof.

[0086] As shown in FIG. 13 (a), the magnetic sensor 120 is mounted on asubstrate 121 having a wiring 122 for connecting a current 200. Due tothe arrangement of the magnetic sensor 120 relative to a magnetic fluxgenerated by the current 200 as indicated by hidden line in FIG. 13(b),the output sensitivity of the magnetic sensor 120 is determined. Thus,by considering the arrangement of the magnetic sensor 120, it ispossible to adjust the output sensitivity of the magnetic sensor 120.

[0087]FIG. 14 shows an example of a structure of a magnetic shield. Amagnetic shield 123 is added to the one shown in FIG. 11. Although theshield has an oval shape here, it is desirable to adjust the shape incorrespondence with the magnitude of the current 200. Reference numeral121 designates a substrate, and reference numeral 122 designates awiring.

[0088]FIG. 15 is a concrete example of the magnetism detection unit. Adetection circuit 110 is incorporated (integrated) into the magneticsensor unit shown in FIG. 11. With this arrangement, it is possible toenhance the S/N ratio of the sensor signal. By internally storingvarious types of corrective data used for automatic calibration asdescribed in FIG. 6 for each magnetic sensor element, the precision canbe further improved.

[0089] Industrial Applicability

[0090] The present invention is applicable to the above-describedover-current protection device, and is also applicable to generalcurrent detection devices for detecting the magnitude of the currentflowing through a conductor, or general breakers for breaking thecurrent when the magnitude of the detected current exceeds apre-determined threshold value.

1. An over-current protection device for shutting off power to a loadwhen an overloaded current flows, comprising: a switching element forswitching a current from a power-supply source to the load, a currentdetector for detecting a current supplied from the power-supply sourceto the load, and a controlling power-supply source for supplying powerto each of the switching element and current detector, wherein saidcurrent detector includes magnetism detection elements having a magneticimpedance effect and corresponding to phases of the power-supply source;AC-current supply means for applying an AC current to each magnetismdetection element through one oscillating means and a first switchcorresponding to each magnetism detection element; bias-current supplymeans formed of bias coils wound on the respective magnetism detectionelements and a third switch for supplying a current to the bias coilsvia the third switch; wave detection means corresponding to themagnetism detection elements for converting an impedance variation intoa voltage and for passing a peak of the voltage; second switchescorresponding to the wave detection means for selecting an output of thewave detection means; holding means for holding the selected voltage ofthe wave detection means; and amplifying means for amplifying thevoltage held by the holding means, and the current for each phase isdetected based on selective operations of the first, second, and thirdswitches.
 2. An over-current protection device for shutting off power toa load when an overloaded current flows, comprising: a switching elementfor switching a current from a power-supply source to the load, acurrent detector for detecting a current supplied from the power-supplysource to the load, and a controlling power-supply source for supplyingpower to each of the switching element and current detector, whereinsaid current detector includes magnetism detection elements having amagnetic impedance effect and corresponding to phases of thepower-supply source; AC-current supply means for applying an AC currentto each magnetism detection element through one oscillating means and afirst switch corresponding to each magnetism detection element;bias-current supply means formed of bias coils wound on the respectivemagnetism detection elements, bias-current applying means, andfrequency-dividing means connected to the oscillating means via a thirdswitch and dividing a frequency output from the oscillating means forsupplying a current having different polarities to the bias coils basedon first and second timings; wave detection means corresponding to themagnetism detection elements for converting an impedance variation intoa voltage and for passing a peak of the voltage; second switchescorresponding to the wave detection means for selecting an output of thewave detection means; first holding means for holding an output of theselected voltage of the wave detection means; two fourth switches forselecting the held voltage based on the first and second timings; twosecond holding means for holding the two selected voltages; andamplifying means for amplifying a difference in outputs of the twosecond holding means, and the current for each phase is detected basedon selective operations of the first, second, third, and fourthswitches.
 3. An over-current protection device according to claim 1,wherein when said first and second switches corresponding to one of themagnetism detection elements disposed in the power-supply phase areselected, said third switch is selected.
 4. An over-current protectiondevice according to claim 1, wherein said oscillating means is operatedsynchronously with the third switch.
 5. An over-current protectiondevice according to claim 1, wherein said controlling power-supplysource comprises at least two power-supply transformers having primaryand secondary coils and connected to a current-supply line linkedbetween the power-supply line and the load, a capacitor for storing acurrent at a secondary side, and a voltage adjuster.
 6. An over-currentprotection device according to claim 1, wherein said controllingpower-supply source comprises a power-supply transformer having at leasttwo primary coils and one secondary coil and connected to acurrent-supply line between the power-supply line and the load, acapacitor for storing a current at a secondary side, and a voltageadjuster.
 7. An over-current protection device according to claim 6,wherein said at least two primary coils and one secondary coil are woundon a single iron core, and said primary coils have different windingturns for each phase.
 8. An over-current protection device according toclaim 7, wherein said two primary coils of the power-supply transformershave a winding ratio of 1:2.
 9. An over-current protection deviceaccording to claim 1, wherein said magnetism detection element, aterminal for applying an AC current to the magnetism detection element,the bias coil, and a terminal for supplying a bias current to the biascoil are integrated with a resin molding process.
 10. An over-currentprotection device according to claim 1, wherein said magnetism detectionelement, a terminal for supplying an AC current to the magnetismdetection element, the bias coil, a terminal for supplying a biascurrent to the bias coil, and a circuit for outputting a signalproportional to an output of the magnetism detection element areintegrated with a resin molding process.
 11. An over-current protectiondevice according to claim 1, wherein said magnetism detection element isformed of a thin-film.
 12. An over-current protection device accordingto claim 2, wherein when said first and second switches corresponding toone of the magnetism detection elements disposed in the power-supplyphase are selected, said third switch is selected.
 13. An over-currentprotection device according to claim 2, wherein said oscillating meansis operated synchronously with the third switch.
 14. An over-currentprotection device according to claim 2, wherein said controllingpower-supply source comprises at least two power-supply transformershaving primary and secondary coils and connected to a current-supplyline linked between the power-supply line and the load, a capacitor forstoring a current at a secondary side, and a voltage adjuster.
 15. Anover-current protection device according to claim 2, wherein saidcontrolling power-supply source comprises a power-supply transformerhaving at least two primary coils and one secondary coil and connectedto a current-supply line between the power-supply line and the load, acapacitor for storing a current at a secondary side, and a voltageadjuster.
 16. An over-current protection device according to claim 15,wherein said at least two primary coils and one secondary coil are woundon a single iron core, and said primary coils have different windingturns for each phase.
 17. An over-current protection device according toclaim 16, wherein said two primary coils of the power-supplytransformers have a winding ratio of 1:2.
 18. An over-current protectiondevice according to claim 2, wherein said magnetism detection element, aterminal for applying an AC current to the magnetism detection element,the bias coil, and a terminal for supplying a bias current to the biascoil are integrated with a resin molding process.
 19. An over-currentprotection device according to claim 2, wherein said magnetism detectionelement, a terminal for supplying an AC current to the magnetismdetection element, the bias coil, a terminal for supplying a biascurrent to the bias coil, and a circuit for outputting a signalproportional to an output of the magnetism detection element areintegrated with a resin molding process.
 20. An over-current protectiondevice according to claim 2, wherein said magnetism detection element isformed of a thin-film.